Updated on 2025-11-06
Planning MIG work on mild steel? Here’s what C25 (75% argon / 25% CO₂) will really cost, plus refill options, typical settings, and safety notes.
As of November 6, 2025 (U.S.), a new 125 CF C25 cylinder typically runs in the mid-$300s when purchased filled, while contents-only refills or exchanges often fall around $75–$80. Actual prices vary by supplier, region, and fees (e.g., hazmat/handling). Owning larger cylinders reduces long-term cost per cubic foot.
Key takeaways
- Expect mid-$300s for a filled 125 CF C25 cylinder; refills/exchanges ~ $75–$80 (regional variance).
- Typical indoor flow rate with C25 is ~20–25 CFH; many guides recommend 25–35 CFH for short-circuit; raise toward 30–35 CFH if you see drafts or porosity.
- Policies differ: some locations refill, others exchange—verify before you buy a tank.
The Cost of 75/25 Welding Gas
When considering the cost of 75/25 welding gas, factor both the initial purchase and refill/exchange expenses. A filled 125 CF C25 cylinder is commonly priced in the mid-$300s range. Refills or contents-only exchanges are often around $75–$80 for a #4/125 CF bottle, with local variance and potential hazmat/handling fees.
If you compare with smaller tanks (e.g., 40 CF), you’ll notice that similar refill fees mean larger tanks usually deliver better long-term value on a cost-per-CF basis.
Common Welding Gases and Their Uses
The 75% argon / 25% CO₂ gas blend, known as C25, is widely used for MIG welding on mild steel. Argon provides an inert atmosphere and smoother arc for cleaner welds; CO₂ increases heat and penetration versus pure argon. Compared with straight CO₂, C25 typically reduces spatter and improves bead appearance.
Typical flow rate: start around 20–25 CFH indoors; many manufacturer guides recommend 25–35 CFH for short-circuit; increase toward 30–35 CFH if you see porosity or feel drafts.
Tank Costs and Refill Expenses
Initial tank prices vary by brand and vendor. Refills/exchanges are highly regional—call ahead for local quotes and fees.
| Tank Size | Typical Initial Cost (filled) | Refill/Exchange (contents) |
|---|---|---|
| 125 CF (#4) | $350–$370 | $75–$80 |
| 80 CF | $300–$450 | $60–$75 |
| 40 CF | See supplier | ≈$60 |
Policy note: many suppliers now prefer exchange over on-the-spot refills, and some are strict about hydrotest dates/markings. Verify their practice before buying a cylinder online.
Example price: 125 CF C25 cylinder (filled) · Example contents price: #4/125 CF exchange
How to Calculate the Real Cost of Welding Gas
- Initial tank cost: budget mid-$300s for a 125 CF C25 cylinder (filled).
- Refill frequency: estimate a contents-only exchange around $75–$80 per cycle for 125 CF.
- Annual total: first year ≈ tank + (refills × price); following years ≈ refills × price.
- Local variation & fees: add for hazmat/handling and hydrotest recert when due.
Quick burn-time math: hours ≈ tank CF ÷ CFH. Example: 125 CF at 20 CFH ≈ ~6.25 hours; at 15 CFH ≈ ~8.3 hours.
Where to Buy or Refill Your Gas
| Method | Typical Cost Pattern | Convenience |
|---|---|---|
| Local suppliers | Contents/exchange fees; cylinder leases or swaps | Fast turnaround; check refill vs. exchange policy |
| Online retailers | Pay once for cylinder (often filled) | Delivery to door; later refill/exchange locally |
Safety tip: store and secure cylinders upright and away from heat/sun. See OSHA guidance on upright storage.
Glossary
- C25
- A shielding gas blend of 75% argon / 25% CO₂ for MIG on mild steel.
- CF / CFH
- Cubic feet of gas in a cylinder / cubic feet per hour flow rate.
- Contents exchange
- Swap your empty cylinder for a filled one of the same size/type.
FAQs
How long does a 300 CF tank of C25 last?
Use volume ÷ flow: 300 ÷ CFH. At 15–20 CFH you’ll get about 15–20 hours; at 25–30 CFH expect roughly 10–12 hours. Actual results vary with technique, leaks, and draft conditions.
Can I mix different welding gases in one tank?
No. Cylinders should be filled by qualified suppliers using certified blends. Never attempt to mix gases yourself; it’s unsafe and can damage equipment or violate regulations.
Is C25 better than other MIG gas mixes?
For mild steel, C25 is a versatile, budget-friendly choice with smooth arc and reduced spatter versus straight CO₂. Other blends (e.g., 90/10) may suit thicker sections or specific transfer modes.
How should I store my welding gas tank safely?
Keep cylinders upright, secured from tipping, in a ventilated area away from heat and sunlight. Close valves and fit caps when not in use.
What should I do if my tank runs out during a project?
Stop, close the valve, and swap to a full cylinder or schedule an exchange. Check for leaks, reset flow to your usual CFH, and make a short test bead before resuming.
